Explanation of multi-condition query in MyBatis
One: Use dynamic SQL to complete multi-condition query
a:Use if+where to implement multi-condition query
First of all, the scenario requirements, there is a grade and class table, the first requirement is Conditional query based on fuzzy query name and age, interface layer method
public List<student> getStudentByIf(student stu);
The second is the configuration of the mapping file
<select id="getStudentByIf" parameterType="stu" resultType="stu">select * from student <where> <if test="stuAge!=0"> and stuAge>#{stuAge} </if> <if test="stuName!=null"> and stuName LIKE '%' #{stuName} '%' </if> </where></select>
Test
studentDao dao = MyBatis.getSessionTwo().getMapper(studentDao.= "z"List<student> list="----------"+
------------zhangyu<br/>---- ------zy<br/>----------zy<br/>----------zhang
<br/>
b: choose when classification
This method is the same as the choose loop structure principle in java. To judge multiple situations, just modify the mapping file
Interface class
public List<student> getAllStudentByLike(Map<String, Object> userMap); //使用map作为参数
Mapping file
<span style="color: #0000ff"><</span><span style="color: #800000">select </span><span style="color: #ff0000">id</span><span style="color: #0000ff">="getAllStudentByLike"</span><span style="color: #ff0000"> parameterType</span><span style="color: #0000ff">="Map"</span><span style="color: #ff0000"> resultType</span><span style="color: #0000ff">="stu"</span><span style="color: #0000ff">></span><span style="color: #000000">select * from student</span><span style="color: #0000ff"><</span><span style="color: #800000">where</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">choose</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">when </span><span style="color: #ff0000">test</span><span style="color: #0000ff">="stuName!=null"</span><span style="color: #0000ff">></span><span style="color: #000000"> stuName like CONCAT('%',#{stuName},'%')</span><span style="color: #0000ff"></</span><span style="color: #800000">when</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">when </span><span style="color: #ff0000">test</span><span style="color: #0000ff">="stuAge!=0"</span><span style="color: #0000ff">></span><span style="color: #000000"> stuAge> #{stuAge}</span><span style="color: #0000ff"></</span><span style="color: #800000">when</span><span style="color: #0000ff">><br/></span><otherwise>
1=1
</otherwise><span style="color: #0000ff"><br/></span><span style="color: #0000ff"></</span><span style="color: #800000">choose</span><span style="color: #0000ff">></span><span style="color: #0000ff"></</span><span style="color: #800000">where</span><span style="color: #0000ff">></span><span style="color: #0000ff"></</span><span style="color: #800000">select</span><span style="color: #0000ff">></span>
Result
zhangyu zy zy zhang
c: There are three ways to use foreach to complete complex queries,
The first one: the parameters passed in are array types
//传一组 xueshengID public List<student> getStudentBystuId_foreach_array(Integer[] ints);
映射文件配置 <!--跟据学生id查询学生Interger-->
<select id="getStudentBystuId_foreach_array" resultMap="studentList">select * from student<if test="array.length>0">where stuId IN/*数组形式传入学生Id*/<foreach collection="array" item="stu" open="(" separator="," close=")"> #{stu}</foreach>
</if>
</select>
Test Class
Integer[] ints = {2,3,4};
List<student> list = dao.getStudentBystuId_foreach_array(ints);for (student item:list) {
System.out.println(item.getStuName());
}
Two: Pass in the list collection
public List<student> getStudentBystuId_foreach_list(List<Integer> list);
<!--跟据学生id查询学生list方式--><select id="getStudentBystuId_foreach_list" resultMap="studentList">select * from student<if test="list.size>0">where stuId IN
/*集合形式传入学生Id*/<foreach collection="list" item="stu" open="(" separator="," close=")">#{stu}</foreach></if></select>
Test:
studentDao dao = MyBatis.getSessionTwo().getMapper(studentDao.class);
Integer ints = 2;
List<Integer> list = new ArrayList<Integer>();
list.add(ints);
List<student> stulist = dao.getStudentBystuId_foreach_list(list);
for (student item:stulist) {
System.out.println(item.getStuName());
}
Third type: Based on Map collection
public List<student> getStudentBystuId_foreach_map(Map<String, Object> stuMap);
<!--跟据学生id查询学生map方式--><select id="getStudentBystuId_foreach_map" resultMap="studentList">select * from student where stuId IN
/*集合形式传入学生Id*/<foreach collection="stuId" item="stu" open="(" separator="," close=")"> <!--collection是自己定义的，就是map的key值-->#{stu}</foreach></select>
<span style="color: #008000"> Map<String ,Object> stumap = new HashMap<String, Object>();
List<Integer> listStuId = new ArrayList<Integer>();
listStuId.add(2);
listStuId.add(3);
listStuId.add(4);
stumap.put("stuId",listStuId);
List<student> list = dao.getStudentBystuId_foreach_map(stumap);
for (student item:list
) {
System.out.println(item.getStuName());
}</span><span style="color: #008000"><br/></span>
Print results You can do the following.
d;Two implementation methods of one-to-many
Mainly due to different configurations in resultMapper
Interface method
public grade getGradeById(int gradeId);
Mapping file configuration
<span style="color: #008000"><!--</span><span style="color: #008000">实现一 对多的第一中实现</span><span style="color: #008000">--></span><span style="color: #0000ff"><</span><span style="color: #800000">resultMap </span><span style="color: #ff0000">id</span><span style="color: #0000ff">="gradeMapOne"</span><span style="color: #ff0000"> type</span><span style="color: #0000ff">="grade"</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">id </span><span style="color: #ff0000">column</span><span style="color: #0000ff">="gradeId"</span><span style="color: #ff0000"> property</span><span style="color: #0000ff">="gradeId"</span><span style="color: #0000ff">></</span><span style="color: #800000">id</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">result </span><span style="color: #ff0000">column</span><span style="color: #0000ff">="gradeName"</span><span style="color: #ff0000"> property</span><span style="color: #0000ff">="gradeName"</span><span style="color: #0000ff">></</span><span style="color: #800000">result</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">collection </span><span style="color: #ff0000">property</span><span style="color: #0000ff">="gatStudent"</span><span style="color: #ff0000"> ofType</span><span style="color: #0000ff">="stu"</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">id </span><span style="color: #ff0000">column</span><span style="color: #0000ff">="stuUd"</span><span style="color: #ff0000"> property</span><span style="color: #0000ff">="stuId"</span><span style="color: #0000ff">></</span><span style="color: #800000">id</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">result </span><span style="color: #ff0000">column</span><span style="color: #0000ff">="stuName"</span><span style="color: #ff0000"> property</span><span style="color: #0000ff">="stuName"</span><span style="color: #0000ff">></</span><span style="color: #800000">result</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">result </span><span style="color: #ff0000">column</span><span style="color: #0000ff">="stuAge"</span><span style="color: #ff0000"> property</span><span style="color: #0000ff">="stuAge"</span><span style="color: #0000ff">></</span><span style="color: #800000">result</span><span style="color: #0000ff">></span><span style="color: #0000ff"></</span><span style="color: #800000">collection</span><span style="color: #0000ff">></span><span style="color: #0000ff"></</span><span style="color: #800000">resultMap</span><span style="color: #0000ff">></span><span style="color: #008000"><!--</span><span style="color: #008000">实现一 对多的第二中实现</span><span style="color: #008000">--></span><span style="color: #0000ff"><</span><span style="color: #800000">resultMap </span><span style="color: #ff0000">id</span><span style="color: #0000ff">="gradeMap"</span><span style="color: #ff0000"> type</span><span style="color: #0000ff">="entity.grade"</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">id </span><span style="color: #ff0000">column</span><span style="color: #0000ff">="gradeId"</span><span style="color: #ff0000"> property</span><span style="color: #0000ff">="gradeId"</span><span style="color: #0000ff">></</span><span style="color: #800000">id</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">result </span><span style="color: #ff0000">column</span><span style="color: #0000ff">="gradeName"</span><span style="color: #ff0000"> property</span><span style="color: #0000ff">="gradeName"</span><span style="color: #0000ff">></</span><span style="color: #800000">result</span><span style="color: #0000ff">></span><span style="color: #0000ff"><</span><span style="color: #800000">collection </span><span style="color: #ff0000">property</span><span style="color: #0000ff">="gatStudent"</span><span style="color: #ff0000"> ofType</span><span style="color: #0000ff">="student"</span><span style="color: #ff0000"> select</span><span style="color: #0000ff">="getStudentById"</span><span style="color: #ff0000"> column</span><span style="color: #0000ff">="gradeId"</span><span style="color: #0000ff">></</span><span style="color: #800000">collection</span><span style="color: #0000ff">> <!--column的值主要作为下次查询的条件，既查询学生的条件--></span><span style="color: #0000ff"></</span><span style="color: #800000">resultMap</span><span style="color: #0000ff">><br/></span>
<select id="getGradeById" resultMap="gradeMapOne">select * from grade,student where grade.gradeId = student.stuGrade and gradeId = #{gradeId}</select><!--ddddddddddddddddddd--><select id="getGradeById" resultMap="gradeMap">select * from grade where gradeId=#{gradeId}</select><select id="getStudentById" resultType="entity.student">select * from student where stuGrade = #{stuGrade}</select><br/>
<br/>
@Testpublic void TestConn(){
gradeDao dao = MyBatis.getSessionTwo().getMapper(gradeDao.class);
grade grade = dao.getGradeById(1); for (student item:grade.getGatStudent() ) {
System.out.println(item.getStuName());
}
}
Both methods can be achieved, the printing effect
Option 1 printing effect
==> Preparing: select * from grade,student where grade.gradeId = student.stuGrade and gradeId = ? ============A sql
==> Parameters: 1(Integer)
<== Columns: gradeId, gradeName, stuId, stuName, stuAge, stuGrade <br/><== 1297, 2, zhangyu, 19, 1<br/>< ;== Row: 1, S1297, 3, zy, 20, 1<br/><== Row: 1, S1297, 4, zy, 21, 1<br/><== Total: 3<br/>zhangyu <br/>zy<br/>zy
Process finished with exit code 0
Option 2 printing effect
==> Preparing: select * from grade where gradeId=? ==========First sql
==> Parameters: 1(Integer)
<== Columns: gradeId, gradeName<br/><== Row: 1, S1297<br/>====> Preparing: select * from student where stuGrade = ? ==========The second sql
====> Parameters: 1(Long)
<==== Columns: stuId, stuName, stuAge, stuGrade
<==== Row: 2, zhangyu, 19, 1
<==== Row: 3, zy, 20, 1
<==== , Row: 4, zy, 21, 1
<==== , Total: 3
<== , Total: 1
zhangyu
zy
zy
Process finished with exit code 0
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